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Development of permanently antimicrobial coatings

Cloete, William Joseph (2011-12)

Thesis (MSc)--Stellenbosch University, 2011.

Thesis

ENGLISH ABSTRACT: Water-borne coatings often contain multiple additives including pigments, dispersing agents,
rheology modifiers, UV stabilizers and biocides. Due to their low molar mass and endocrinedisrupting
properties, many of these additives, upon leaching from the substrate film, with time
pollute water systems and become hazardous to the environment and to human health. In this study,
I aimed to develop a facile method for the production of a polymeric biocide to serve as alternative
to low molar mass biocides used in water-borne coatings. A secondary aim was to show that,
without additional modification, the polymeric species can be used in surfactant-free ab initio
emulsion polymerizations.
Using a two-step process, I modified a commercially available copolymer, poly(styrene-alt-maleic
anhydride) (SMA 1000), with mixed amines in order to obtain latexes with inherent antimicrobial
activity. In the first step, I reacted SMA 1000 with 3-dimethylamino-1-propylamine and aqueous
ammonia to confer antimicrobial activity and water-solubility to the SMA copolymer. In the second
step, the copolymer was incorporated into a film-forming styrene-butyl acrylate (STY/BuA) latex.
The modified SMA was incorporated into a latex in two ways: (1) post-added to the latex, and (2)
used as stabilizer in emulsion polymerization. In both cases, the latex remained stable for up to 11
months, and stability was probably due to steric stabilization of the polymer particles. Antimicrobial
activity of the latex film was achieved with both methods. When the modified SMA was post-added,
antimicrobial activity was restricted to specific areas on the eventual polymer film, and when
modified SMA was used as stabilizer, antimicrobial activity was evenly distributed throughout the
polymer film.
Fluorescence microscopy showed homogeneous distribution of antimicrobial activity upon
inoculation in Gram positive bacteria dispersions when the modified copolymer was used as
polymeric stabilizer for the synthesis of STY/BuA latexes. No antimicrobial activity against Gram
negative bacteria was achieved. The homogeneous distribution of antimicrobial activity throughout
the film was a result of adsorption of polymeric biocide/stabilizer to each individual latex particle.
With further commercial development, high molar mass copolymers modified for antimicrobial
activity may be a feasible, environmentally-friendly and healthy alternative to be used as stabilizers
in emulsion polymerizations to produce water-borne coatings.